Some painting programs allow an existing digital image to be rendered in a selected style. For example, Adobe Photoshop 5.0 offers filters that apply artistic styles, such as simulated watercolor, pastel, dry brush, or fresco, to a digital image. Photoshop and other programs, such as Xaos Tools' Paint Alchemy, also enable the application of brush styles in rendering an image. These filters and effects apply algorithms uniformly (possibly with some randomness) to all parts of the image.
Another painting program, Fractal Design's Painter 5.0, allows a user to apply realistic-looking brush strokes to a digital canvas. The strokes are applied in much the same way that a painter would brush paint on a canvas. The user may create almost any painting that he is capable of drawing. To create a good painting, the user must have artistic ability.
A variety of other approaches to rendering painterly images have been used and proposed. For example, fluid brush strokes may be automatically applied to an entire image in a selected painting style. In another technique, a grayscale image may be converted into a pen-and-ink style line drawing by allowing interactive modification of image tone (lightness, darkness) and a line stroke direction field. In a different approach, realistic watercolor brush marks may be applied to a digital image automatically based on an initial painting condition specified by a user. In another system, parametric surfaces may be rendered in pen and ink based on a three-dimensional model of objects to be rendered.